Growth of YBaCuO single-domains up to 7 cm (original) (raw)
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Isothermal growth of large YBa2Cu3O7−x single domains up to 93 mm
Physica C: Superconductivity, 2000
The growth of YBa2Cu3Oz.x single domains larger than 30-40 mm by a classical Top Seeding Melt Texturing (TSMT) method appears to be difficult. Because of the very narrow solidification range between the onset of the nucleation from the seed and the nucleation of grains in the liquid, reaction with the substrate as well as uncontrolled thermal gradients introduce severe limitations to the growth. After suppressing nucleation from the substrate and improving the temperature homogeneity around the sample, the growth rate measured in situ was used to carefully adjust the process. A YBa2Cu307.x single domain has been grown up to 93 mm without applied thermal gradient nor large overheating. The texture is confirmed on a large volume by neutron scattering and an homogeneous 211 size distribution and content are found across the sample. This suggests that steady growth conditions have been maintained and that even larger samples could be grown.
Isothermal growth of large YBaCuO single domains through an artificial array of holes
Journal of Crystal Growth, 2005
For various applications, single domains (centimetric crystals with defects) of the YBa 2 Cu 3 O x superconductor oxide are grown using the top seeding melt growth (TSMG) method. During the oxygen annealing inducing superconductivity, cracks open at the surface layer and propagate into the bulk. Since the cracking can be reduced on thin samples, we proposed to grow single domains with thin wall geometry prior to oxygenation.
Growth shape of melt-textured YBaCuO crystal
Journal of Crystal Growth, 1995
A growth shape of the melt-textured YBa2Cu3Oy (1-2-3) domain was constructed with two-and three-dimensional shapes of the local parts of the 1-2-3 domain. The 1-2-3 domain has a polygonal shape with a square pyramid consisting of stepped terraces at the top and a tetragonal columnar body. X-like linear traces are observed on the surface of the 1-2-3 domains, which often meet at the corners and the center of the plane. The melt-textured 1-2-3 domain is believed to be a single-crystalline body including some microstructural defects such as microcracks, entrapped liquid phase and YzBaCuO5 inclusions.
Nucleation and growth mechanisms of textured YBaCuO and the influence of Y2BaCuO5
Physica C-superconductivity and Its Applications, 1994
123 texturation has been achieved with success on Y203 without application of an external thermal gradient for the purpose of a better understanding of nucleation and growth mechanisms. We have studied the effects of thermal parameters such as the maximal applied temperature and crystallization speed. Their respective contributions to the peritectic recrystallization (211 consumption), and to the textured domain size have been made precise by using X-ray data and semi-quantitative analysis on the micrographs. The interface reaction between the Y203 substrate and 123 has been analyzed. The substrate promotes a seeded type growth of 123 owing to an interracial 211 layer. The mechanism of crystallization has been analyzed in the light of existing theoretical models. Our data confirm a crystallization of 123 directly from a liquid as in a peritectic reaction where a major part is played by the yttrium diffusion in the liquid. Y atoms are supplied by the dissolution of 211 particles. According to Uhlmann-Chalmers-Jackson (UCJ) theory, coarsened 211 grains are trapped by the solidification front in contrast to particles smaller than a critical radius that are consumed in the peritectic reaction. (This process explains why such large 211 particles are obtained in MTG contrary to QMG or MPMG methods. ) Moreover, EPR results show a preferential orientation of 211 inclusions according to the 123 matrix which could be favorable to flux pinning in the superconducting state. 211 oriented inclusions make possible, to some extent, heterogeneous nucleation at platelet-211 junctions. On the other hand, microstructural studies show that the liquid/solid interface is rather unstable being frequently cellular or dendritic, consistent with a model proposed by .
Isothermal melting and continuous isothermal melt texturing of YBaCuO
IEEE Transactions on Appiled Superconductivity, 1993
Absrtact-Considerable research activity centres on techniques for the fabrication of highly textured polycrystalline YBCO. One established technique is Melt Texwed Growth, in which slow cooling in a temperature gradient results in directional solidification at a growth front. We report a study of Isothermal Melt Texturing where the 02 partial pressure dependence of the melting point of YBCO is exploited to substitute for the slow cooling and temperature gradient of the Melt Textured Growth method. A melt-pool is produced by lowering the 0 2 partial pressure locaHy with a jet of Ar directed onto the centre of a YBCO slab within an 0 2 filled furnace and itq development is investigated as a function of temperature, Ar/02 ratio and time. If the pool is allowed to cool slowly, a large grained microstructure is formed, with 123 crystals of around lmm average cross section. The critical current density is around 2000A~m-~ at 77K (B=OT). In a further set of experiments the jet is driven slowly across the surface, melting a track. When the jet moves sufficiently slowly, a large grained microstructure is formed by continuous, isothermal processing.
Physica C: Superconductivity, 1998
Parameters affecting the nucleation and growth of a Y123 single-domained crystal were studied in top-seeded melt processing. Based on the parametric study, the two-step undercooling technique was developed. The key points techniques are the controlled nucleation of Y123 at the primary undercooling step and the accelerated growth at the secondary undercooling temperature. Optimization of the process parameters in the two-step undercooling technique considerably reduced the processing time required for the growth of the Y123 single crystal without degradation of the levitation property.
Physica C: Superconductivity, 1995
Microstructures near the domain boundary were investigated in the YBa2Cu307_y(Y123) samples melt-textured in air atmosphere. It is found that the free CuO phase is often observed near the domain boundaries of the Y123 samples, probably due to the variation of the composition of the finally solidified liquid phase. Also, the effect of excess CuO on the microstructure of the domain boundary was investigated in the Y123 melt-textured with 5 wt.%-20 wt.% CuO addition. When the amount of the CuO is small, CuO phase exists as a discrete form at the domain boundaries. As the CuO content increases, spherical CuO pockets and large CuO pools containing unreacted Y211 particles are developed. In addition, the CuO addition changes the growth morphology of the Y123 domain; from a planar mode to a Y123/CuO cellular structure with increasing CuO content.
Subgrain formation, 211 particle segregation and high-angle 90° boundaries in melt-grown YBaCuO
Physica C-superconductivity and Its Applications, 1997
Microstructural features such as subgrains, Y2BaCuO5 particles, and high-angle boundaries were studied in single- and multiple-domain melt-textured YBaCuO levitators. Subgrains elongated in the c- or a-direction and rectangular in cross section were formed during solidification by cellular growth. Formation of subgrains by combination of a- and c-growth was also observed. Their boundaries were predominantly low-angle, and were not cracked or wetted by second phases. Macrosegregation of Y2BaCuO5 particles developed mainly in the regions formed by c-axis growth. The segregation is related to Y2BaCuO5 particle pushing by the YBa2Cu3O7−x growth front. The structure of 90° high-angle grain boundaries appeared to be similar to that of the low-angle grain boundaries.
Direct observation of textured YBa2Cu3O7−δ crystal growth from the melt
Physica C: Superconductivity, 1992
The behavior and kinetics of textured growth of the YBaZCu@_d (123) compound from Y,BaCuO, (21 I) +liquid have been investigated by hot-stage optical microscopy and high-temperature x-ray diffraction methods. The formation of the 123 is found to begin in the liquid of the peritectic melt, not nucleated from 2 11 crystals as is widely assumed. The quantity of the liquid phase strongly influences the crystal growth and final morphology of the 123. Dynamic studies show that the optimum temperature for 001 orientation of 123 is 940°C on an MgO substrate. The growth rate of 123 from the melt is rapid; the rate constant was determined to be 0.526x 10m2 s-l.
Crystalline growth rate and microstructure in YBaCuO thin films
Physica C: Superconductivity, 2001
The in¯uence of the anisotropy of the crystalline growth rate on the microstructure and morphology of YBaCuO thin ®lm deposited by laser ablation is studied by means of transmission electron microscopy. The results obtained from high resolution lattice imaging and large angle convergent beam diraction, together with the investigations of the thin ®lm surface morphology show the strong in¯uence of the dierent crystalline growth rates on both the internal stress present in the YBaCuO ®lm and the roughness of the outer surface. These results should be of prime importance for the superconducting properties. This is an essential in tailoring these thin ®lms for device applications.